1. Field of the Invention
The present invention relates generally to the field of semiconductor fabrication, and more particularly to a susceptor for securing a wafer in a processing chamber.
2. Description of the Prior Art
Semiconductor processing and similar manufacturing processes typically employ thin film deposition techniques such as Chemical Vapor Deposition (CVD). In CVD processing, as well as in similar manufacturing techniques, a substrate such as a silicon wafer is secured within a processing chamber by a susceptor and exposed to the particular processing conditions of the process. The susceptor is essentially a pedestal that, in addition to securing the substrate, can in some instances also be used to heat the substrate.
FIGS. 1–3 illustrate a representative series of fabrication steps for forming a susceptor according to the prior art. In FIG. 1, conductive elements 102 are set between layers 104 of a ceramic material, such as AlN. The conductive elements 102 can be, for example, a heating element and a static plate for maintaining an electrostatic field. Conductive elements 102 have to be electrically connected to, for example, power supplies and voltage sources, and towards this end, each conductive element 102 includes an electrical contact 106. Once the conductive elements 102 with their respective electrical contacts 106 have been set between layers 104 of the ceramic material, the entire assembly is sintered or hot-pressed to form a substrate support 108.
Once the substrate support 108 has been sintered, a hole 202 is machined into the substrate support 108 to create access to the electrical contact 106 of each conductive element 102. Typically, the hole 202 includes a threaded surface. Next, as shown in FIG. 3, a contact 302 is threaded into the hole 202 and brazed to the electrical contact 106. A support shaft 304 is also coupled to a bottom surface of the substrate support 108. The support shaft 304 serves to both elevate the substrate within a processing chamber as well as to act as a conduit for electrical connectors such as the contact 302. Accordingly, an extension rod 306 of the contact 302 extends through the support shaft 304 to electrically connect to a voltage or power supply (not shown) of the processing chamber.
Through extended use, deficiencies in the connection of the contact 302 to the conductive element 102 have come to light. In particular, a braze material 310 that connects the contact 302 to the electrical contact 106 is a weak point that is prone to fail. Two common failure mechanisms include mechanical failure and corrosive failure. Mechanical failure can occur due to various sources of stress. For example, repeated coupling and decoupling of the extension rod 306 to the voltage or power supply of the processing chamber can transfer stresses to the braze material 310. Additional stresses are created by repeated heating and cooling cycles. Corrosive failure occurs when corrosive process gases, such as chlorine, fluorine, and oxygen, migrate between the contact 302 and an interior wall of the hole 202 and corrode the braze material 310. It will be appreciated that in many instances both failure mechanisms contribute to the ultimate failure.
Therefore, what is needed is a susceptor with internal electrical connections that are better able to withstand mechanical stresses and corrosive environments.